Fearless

Ruth Fremson/The New York TimesMarine iguanas huddled together for warmth on volcanic rock on Tintoreras island in the Galápagos in 2009.

Among biologists, the Galápagos Islands — an archipelago of volcanic islands that straddle the equator about 600 miles from the coast of mainland Ecuador — are legendary. For when the young Charles Darwin sailed around the world in the 1830s, he visited these islands, and was struck by five things.

First, he observed that many of the animals and plants living in the Galápagos are found nowhere else in the world. Examples? Marine iguanas, which swim, eat algae and spend hours basking on the rocks. Darwin, uncharitably, described them as “hideous” and “stupid.” Then there are the giant tortoises (“antediluvian,” said Darwin), the largest of which can weigh as much as 250kg, or 550 pounds. Among the birds, there are flightless cormorants, which have stumpy little wings; and, famously, there are several unique species of finch.

Darwin’s second observation was that certain sorts of animals are missing. The islands have no frogs, for example, and until humans came, there were no land-lubbing mammals like rats or cats. Third, he noted that many of the creatures living in the Galápagos resemble, but differ from, those of the nearest continent — South America. Fourth, the inhabitants of one island often differ from those of another.
These four observations formed an essential piece of Darwin’s evidence that evolution takes place. Remote volcanic islands can only be reached by certain sorts of life forms — those that can cross hundreds of miles of ocean without perishing. So: birds and bats can fly there. Reptiles, many of which can go for months without eating or drinking, can float there on driftwood. Frogs, in contrast, are killed by salt water, and have no way to travel across the sea. Once the organisms arrive in the new place, they begin to evolve to better cope with their new environment; over time, they start to diverge from their cousins on the mainland (and, in some cases, from their cousins on the other islands), producing the patterns that Darwin observed.

Ruth Fremson/The New York TimesA young giant tortoise crossing a road on Isabela island in the Galápagos, 2009.

But the fifth thing that Darwin noticed in the Galápagos is, to the casual visitor, by far the most striking. It’s the tameness of the animals. Darwin reported that he would often stride up to the giant tortoises and sit on their backs; after he administered “a few raps on the hinder part of their shells, they would rise up and walk away.” He picked up marine iguanas and tossed them into the ocean; he pulled the tail of a land iguana (“it was greatly astonished . . . and then stared me in the face, as much as to say, ‘What made you pull my tail?’”). And, of the birds, Darwin wrote, “All of them approached sufficiently near to be killed with a switch, and sometimes, as I myself tried, with a cap or hat.”

Riding giant tortoises is now prohibited; so is the sport of toss-the-iguana. And, needless to say, you are not allowed to kill birds with, or without, your hat. You are, however, allowed to photograph them.

And you don’t need a fancy zoom lens to take amazing pictures. Mockingbirds, warblers and sea lions come right up to you, and in places, it’s hard not to step on the marine iguanas: they don’t get out of the way. It’s weird. So much so that it’s almost tempting to believe that all the animals are, in fact, clockwork toys, wound up every night by employees of the Ecuadorian tourist board and positioned so as to amaze the gawking visitors.

So why are the animals so tame?

No one knows for sure. But in general, animals tend to be more tame — less prone to fleeing from people — on islands than they are on continents. In Australia, island wallabies let humans come closer to them than mainland wallabies do; similarly, on an island in the Gulf of California, iguanas allow closer approach than their mainland cousins will tolerate.

The reason for this is that islands are (usually) safer places to live. Islands are typically home to fewer predators — especially cats and other mammals — than the mainland, so animals that live there are at less risk of becoming somebody’s lunch.

In a dangerous environment, being a skittish creature can save your life. But in a safe environment, where you are unlikely to be pounced on, such behavior is a costly waste of time and energy. After all, running away uses calories that could be spent on other activities; hiding in a burrow means time not eating, seducing or basking in the sun. (Although sunbathing is usually thought of as something lazy, for many animals it serves an important purpose: reptiles like lizards and iguanas raise their body temperatures by lying in the sun, and cormorants, which don’t have oil on their feathers the way ducks do, sunbathe to dry themselves after fishing.)

In the absence of predators, then, skittish individuals are at a disadvantage, and are likely to leave fewer offspring. Over time, populations would come to be composed of more fearless creatures. (This situation obviously creates great vulnerability should predators then appear.)

Michael Nagle for The New York TimesA blue-footed booby on Santa Cruz island in the Galápagos in 2007.

In the Galápagos, there has been plenty of time. The islands are several million years old, and for most of this, they would have been a pretty safe place to live. To be sure, things changed around 400 years ago, when pirates and whalers began stopping there to get provisions; but even with this, compared to most islands, the Galápagos have been remained relatively pristine. (This is through both luck and energy. Luck: these islands weren’t settled in the same way that most other islands were. Even now, only 3 percent of the land is inhabited. Energy: in recent years, big efforts have been made to get rid of rats, goats and other pests.)

If Darwin were to visit today, he might be annoyed that tortoise riding is forbidden. But he would still be struck by the tameness of the animals.

Notes:

I have taken Darwin’s descriptions of the animals he meets in the Galápagos from chapter 17 of his travelogue, “The Voyage of the Beagle.” Mine is the Meridian edition, published in 1996, with an introduction by Walter Sullivan. The marine iguanas are described as hideous and stupid on page 333; iguana-tossing is related on page 335. Giant tortoises are impugned as antediluvian on page 324; Darwin describes riding them on page 332. He tells us of pulling the tail of the land iguana on page 336, and of killing birds on page 344 (he devotes a special section to the tameness of the birds). All of his evolutionary observations on the Galápagos are also given in this chapter; he elaborates on them further in chapter 12 of the “Origin of Species” (first edition).

My account of the evolution of fearlessness is a simplified account of a more complex phenomenon: most animals have a suite of anti-predator responses, some of which will be hard-wired (i.e., genetic), and some of which will be learned. Different aspects of anti-predator behavior can thus be lost at different rates.

Disclosure: my trip to the Galápagos was supported by the Aspen Institute. Thanks, too, to Jerry Coyne, Elizabeth Jones and Jonathan Swire for interesting discussions on the evolution of animal tameness.

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Olivia Judson, an evolutionary biologist, writes every Wednesday about the influence of science and biology on modern life. She is the author of “Dr. Tatiana’s Sex Advice to All Creation: The Definitive Guide to the Evolutionary Biology of Sex.” Ms. Judson has been a reporter for The Economist and has written for a number of other publications, including Nature, The Financial Times, The Atlantic and Natural History. She is a research fellow in biology at Imperial College London.